In 1966 Dinah Williams handed over the family farm to her daughter, who created Rachel's Organic.

Dinah Williams, who has died aged 98, was a pioneering member of the Soil Association and the first in Britain to register her farm, Brynllys, to be a certified organic dairy farm. In 1952 she had attended a lecture given by Eve Balfour, author of The Living Soil, and this proved to be a turning point. Balfour's book argued the case for a more sustainable system of agriculture and led to the formation of the Soil Association. Dinah joined, although she had long since practised many organic principles, at a time when the government was challenging farmers to intensify production.

Dinah was born in Aberystwyth, the second of three children of Abel Jones, Professor of Agriculture at Aberystwyth University, and his wife, Bessie, the university's first Dairy Instructress. Both encouraged Dinah's interest in farming from the day they read her school essay entitled "I want to be a farmer". Many years later she recalled her feelings: "Nothing deflected me then and nothing has deflected me since."

That single-minded ambition was to colour her life from the age of 12, when her father died of leukaemia, leaving her mother to farm on her own. Dinah never forgot the hardships her mother faced during the worsening depression of the 1920s. Following her schooldays and a short course in agriculture at the university, she determined to return to work with her mother, a firm believer in what she termed natural farming. Their relationship matured, as mother and daughter, teacher and pupil. When I asked Dinah later whether she always agreed with her mother on farming matters, she replied: "Oh no, but she was good, you know." Then her face lit up with a warm reflective smile: "What she said usually worked and that never bothered me."

Bessie's guidance was pivotal. At their farm, Nantllan, in the Clarach valley close to Cardigan Bay, the emphasis was on milk production from a herd of Guernsey and Ayrshire cows. Every cow was tested for tuberculosis, the scourge of the time, and each morning the farm delivered clean bottled milk, cream and yoghurt direct to customers at Aberystwyth. Bessie was an entrepreneur and scorned the coming of the Milk Marketing Board in 1933. She was sceptical about mixing her rich, clean Guernsey milk with milk from other herds.

Dinah's aptitude for learning impress- ed her mother and she gave her the opportunity of joining a party led by Sir John Russell, the inspirational director of the Rothamsted agricultural research station, to Ukraine, a visit that opened her eyes to other farming practices and repressive state systems.

At the end of the 30s Dinah fell in love with Stanley Williams; their marriage began in a smallholding near Borth, just north of Aberystwyth, and it prompted Bessie to retire, leaving the Clarach farm to her son Sandy. At the end of the second world war, Stanley and Dinah moved to Brynllys, a larger farm of some 150 acres, and it was here that Dinah was able to develop her own ideas.

She bred a prize-winning herd of pedigree Guernsey cows; she became an acknowledged judge of cattle; she used the newly developed strains of grasses, particularly S23, with the right mixture of clovers to enrich the soil; she carefully managed new composting techniques which ensured an organic fertiliser; and a mix of old meadows and new leys became the basis for rotational grazing. To the conventional farming fraternity, the Williamses were cranks and eccentrics, and their methods were dismissed as "muck and magic".

Her marriage, and four children, a boy and three girls, brought Dinah a deep happiness but as they approached their silver wedding anniversary, Stanley died and she lost "a tolerant man and a peacemaker". She transferred the running of Brynllys to her daughter Rachel and son-in-law Gareth in 1966, and there they went on to develop Rachel's Dairy (Rachel's Organic), but Dinah's work was far from finished.

She became an active member of the Grassland Society, an activist within the National Farmers' Union, and president of the Guernsey Society. Her contribution to pedigree livestock breeding was acknowledged in her appointment to the Welsh Agricultural Artificial Insemination panel. She was also appointed Fellow of the Royal Agricultural Society, one of the very few women to have received the honour.

Forthright and resolute in agricultural policy discussions, Dinah challenged academics and politicians if she considered their arguments flawed, but she was kind and inspirational to the young. She was active to the end of her long life, taking a cold bath each morning, followed by a walk around the farm. She was passionate about the role of nutrition in health and the importance of good food. "The whiter the bread, the sooner you're dead," was one of her favourite sayings, and her agricultural philosophy was based on the tenet: "In farming you have to leave the land in better heart than when you inherit it and for that you have to work hard and be disciplined."

I spent many hours in her company during the last three years, researching a book chronicling her family history. She was always gracious and informative, but when I touched on topics such as intensive farming, GM crops or even feminism, she would fix me with a steely gaze: "You see, our generation was a much harder generation of women. That makes for character."

Her great joy was her family, and she was proud of the success of Rachel's Dairy. She reflected: "I hope I've been supportive, I think I have."